This invention relates to a glass production method, and more particularly to a method of preparing molten glass as an indispensable step in the production of glass by utilizing waste glass as part of the ingredients.
In the production of glass and particularly of plate glass, it is usual to utilize pulverized waste glass as part of the starting materials. Besides an economical effect, remelting of waste glass aids in melting of other raw materials. In the case of using cullet or ordinary plate glass there is little problem so long as the amount of the reused cullet is not so large as unfaborably affects the quality or properties of the product. It is possible to reuse pulverized cullet of plate glass by premixing it with other raw materials and throwing the mixture onto the surface of molten glass in a furnace or tank.
Reuse of waste glass is made also in the production of glass bottles. In this case, however, there is an inconvenience that if an organic substance such as synthetic resin used as reinforcing coating on glass bottles remains adhered to the waste glass there occurs coloring of the produced glass in a brownish color as is commonly called carbon amber. Accordingly, there is the need of sorting recovered waste glass to avoid the reuse of scrap glass contaminated with an organic substance. A similar inconvenience is experienced also in the production of glass fiber. A large amount of industrially produced glass fiber is utilized in the form of mat or felt comprising an organic binder. If waste glass fiber contaminated with an organic binder is remelted together with other raw materials of glass fiber, the resultant molten glass tends to be colored irregularly and, furthermore, tends to become nonuniform in viscosity and/or involve bubbles, so that difficulties are offered to the succeeding spinning operation.
Furthermore, there is another problem about reuse of waste glass fiber. When waste glass fiber is put into the melting tank together with a mixture of other raw materials of glass, meaning that the reused glass fiber and the raw materials undergo melting in a mixed state, remelting of the glass fiber proceeds so rapidly because of its thinness in diameter that melting of the raw materials through a vitrification reaction is obstructed by the remelted glass. As a consequence there arises a possibility that the presence of unmelted raw materials in the molten glass causes errosion of platinum parts such as bushings formed with spinning orifices, even aside from the aforementioned unfavorable phenomena attributed to the presence of an organic substance in the reused waste glass fiber.
For these reasons, it has been deemed impractical to industrially reuse waste glass fiber, and therefore waste glass fiber has mostly been dumped.